We are defining T-cell subpopulations distinguishable on the basis of cell surface markers that are involved in the generation of killer cells directed against alloantigen or TNP altered syngeneic targets. We are particularly interested in a T-cell subpopulation that expresses an H-2IA encoded marker. These T-cells are required to generate effectors and serve in a regulatory capacity. We plan to define their roles more precisely in the production of soluble help. We have preliminary evidence for three characteristics of soluble helper activity, nonspecific, TNP specific and H-2 restricted help. Further characterization of these activities is planned. Helper factor supernatants (HFS) are derived from alloantigen-activated murine lymphocytes. These HFS also augment the generation of cytolytic effector cells to syngeneic tumor cells. The effects are dose dependent and vary with the syngeneic tumor system under study. The effector cells generated are specific for the tumor associated antigen(s) utilized for their induction and are sensitive to lysis with anti-T-cell serum but are insensitive to lysis with an allogeneic anti-NK cell serum. The effects of purified helper factor will be studied in these systems as well as the relevance of Ia bearing regulatory T-cells.